1. Field of the Invention
The invention relates to the field of digital color image processing and especially to white balancing of a digital image.
2. Description of the Prior Art
The human eye can adjust to varying illumination conditions. Digital images should undergo a compensation process that is known as white balancing in order to adjust digital images to varying illumination conditions. This process is referred to as white balancing because its goal is to represent white objects as white, despite the illumination conditions.
Some prior art white balancing methods are highly complex and require computational resources that are available only in costly hardware, other prior art methods process the whole digital image and are time consuming. Various prior art methods and systems for white balancing are described in the following patents and patent applications, all being incorporated herein by reference: U.S. Pat. No. 7,151,563 of Masayu, U.S. Pat. No. 6,873,727 of Lopez et al., U.S. Pat. No. 7,006,135 of Ishimaru et al., and U.S. Pat. No. 6,839,088 of Dicarlo et al.
One prior art white balancing method involves looking for pixels that can be attributed to an illumination of a gray object. This includes looking only into pixels that fall within an oriented gray gamut. This oriented gray color gamut is usually a hull convex polygon that is tilted in relation to the horizon. It is noted that these pixels can result from imaging one or more gray objects under certain lighting conditions as well as from imaging non-gray objects under other lighting conditions.
The reliability of the abovementioned prior art white balancing method is strongly dependent upon a number of pixels within the tilted gray gamut and to the colors of the imaged objects. A low reliability can be obtained if, for example, most or all of the imaged objects are not gray and, additionally or alternatively, if due to illumination conditions there are few pixels that fall in the oriented gray gamut.
There is a growing need to provide a robust and reliable white balancing method, device, and computer program product.